This invention relates in general to a receiver sheet transport for use in an electrographic copier, and more particularly to apparatus including an improved transport for successively moving a receiver sheet into alignment with related transferable marking particle images on a moving member for transfer of such images seriatim from the member to the aligned sheet in accurate superimposed register.
In making multicolor reproductions (copies) with a plain paper electrophotographic copier, for example, a multicolored document is illuminated to provide color separation images of the document. The color separation images expose a charged photoconductive member, at spaced image-receiving areas along the member, to form latent image charge patterns on the member corresponding to the respective color separation images. The latent image charge patterns are developed with appropriately colored marking particles (toner) to form transferable images. The transferable images are transferred from the photoconductive member to a receiver sheet in superimposed register to form a multicolor reproduction of the multicolor document.
In order to transfer the transferable images from the image-receiving areas to the receiver sheet in superimposed register, the receiver sheet is moved in a path to repetitively bring the sheet into transfer relation with the photoconductive member at a transfer station. In the aforementioned U.S. patent application Ser. No. 353,779, apparatus is disclosed which includes a transport for successively moving a receiver sheet into transfer relation with related transferable images in the image-receiving areas on the photoconductive member for accurate superimposed register of images transferred to the sheet. A corona transfer charger effects transfer of such images seriatim from the member onto such receiver sheet. The transport employs a tow bar having vacuum plenums for capturing the lead and trail edges of a receiver sheet so that a portion of the sheet intermediate the lead and trial edges is self-supporting. The tow bar does not block the field of the corona transfer charger during transfer, and the self-supporting portion of the receiver sheet conforms to the photoconductive member during transfer to prevent positional misregistration between subsequent images transferred to such sheet. The use of vacuum for capturing the lead edge, however, does not insure that the receiver sheet is in accurate alignment with the image-receiving areas of the photoconductive member. Accordingly, while the transferable images are transferred to the receiver sheet in accurate superimposed register, the resultant reproduction may not be properly positioned on the receiver sheet. In the aforementioned U.S. patent application Ser. No. 353,778, an improved transport is disclosed which securely clamps the lead edge of the receiver sheet in alignment with the head edge of an image-receiving area of the photoconductive member. However, in such transport the clamp does not effect positive release of the receiver sheet after transfer is completed.